Stone or plate for photomechanical and for other purposes, and method of preparing same.



GERALD FORTESCUE VVETHERMAN AND GEORGE HOLZHAUSEN, OF ENFIELD, ENGLAND.

STONE OR PLATE FOR PHOTOMECHANICAL PRINTING AND FOR OTHER PURPOSES, ANDMETHDD 0F PREPARING SAME.

SPECIFICATION forming part of Letters Patent No. 707,747, dated August26,1902.

Application filed January 31, 1902. Serial No. 92.075. (No model.)

To all whom it may concern.-

Be it known that we, GERALD FORTESCUE WETHERMAN, printer, a subject ofthe King of England, and GEORGE HoLzHAUsnN, foreman, a subject of theGerman Emperor, both residing at Enfield, in the county of Middlesex,England, haveinvcnted a certain new and useful Stone or Plate forPhotomechanical Printing and for other Purposes, and Method of Preparingthe Same, of which the following is a specification and which wasoriginally included in application, Serial No. 84,895, filed December 5,1901.

In preparing sensitive plates, stones, or the like for printing and forother purposes great difliculty is experienced in so coating the stones,&c., as to produce an absolutely-even layer of sensitive material on theentire surface. If, however, the coating varies in several parts, thegrain will also be unequal and the ultimate product (say a transfer or adirect print) will not be as satisfactory as. is desirable.

According to the present invention we sensitize a plate, stone, or thelike as follows: We prepare,firstly, an emulsion, composition, ormixture the base of which is gelatin sensitized by a chrome compound-saythe following: Stock solutions: No. 1, twenty per cent. solution ofcalcium chlorid; No. 22, ten per cent. solution of chrome alum; No. 3,twenty per cent. solution of ferricyanid of potassium; No. 4, twenty percent. solution of chlorid of zinc; No. 5, one hundred grams of gelatindissolved in five hundred cubic centimeters of water; No. 6, ten gramspotassium bichromate and fifteen grams of ammonium bichromate dissolvedin one hundred cubic centimeters of Water. In making No. 5 solutiondissolve the gelatin in the water by means of a hot-water bath and whencompletely dissolved add the whole of No. 6 solution, then mixthoroughly and add forty cubic centimeters No. 1, ten cubic centimetersNo. 2, five cubic centimeters No. 3, and five cubic centimeters No. 4solution. When thoroughly mixed, heat the mixture to a temperature ofcentigrade and filter. We then take a quantity of this sensitizing mixofthe plate and which will causethe grain also to be uniform over theentire surface.

In some cases instead of using the above sensitizing mixture we use thefollowing to obtain a variation in the grain.

The effect of the two solutions does not materially differ; but it willbe found that with some subjects one will work better, with some theother, though it is not possible to lay down a theory or fixed rulethereon. A little practice is the only guide in this as in allphotographic manipulations, and the use of either solution depends onthe grain required, the following giving, as a rule, a somewhat-coarsergrain than the first:

Stock solutions: No. 1, twenty per cent. solution of chlorid ofpotassium; No. 2, twenty per cent. solution chlorid of calcium; No. 3,one hundred grams gelatin dissolved in four hundred cubic centimeters ofwater; No. 4, ten grams each of potassium bichromate and ammoniumbichromate dissolved in fifty cubic'centimeters of water. I

Dissolve the gelatin as described above. Mix No. 3 and No. 4 togetherand add to the mixture twenty-five cubic centimeters of No. 1 andtwenty-five cubic centimeters of No.2.

\Vhichever of the two mixtures we employ we prefer to prepare thesurface to be sensitized as follows:

Clean the surface carefully by the usual methods. Then coatit with thefollowing: Mix one ounce of silicate of potash, one-half grain oftannin, and ten ounces of beer. The addition of tannin is important, asthe tannin causes close and firm adherence of the priming on the glassand of the film on the priming. With this mixture the surface to besensitized is coated, say, by flooding it, then allow it to dry. Thiswill cause the sensi- 1ngt'. e.,-the dilute sensitizerand proceed tocoat with sensitizer of full strength. When coated, the plate or stoneis dried at a temperature of from 50 to 60 centigrade. When dry, it isready for exposure under the negative.

By using first a very dilute sensitizer and then before this dries anundilute sensitizer the coating over the whole surface of even thelargest platessay thirty by fortywill be absolutely even andhomogeneous, so -that the sensitiveness is in all parts equal andthegrain ultimately'produced will also be equal in all parts,as the thincoating causes the undilute to take Well and combines with it perfectly.

What we claim, and desire to secure by Letters Patent of the UnitedStates, is-

1. A process of sensitizinga stone, plate or the like by applying,thereto first a dilute sensitizing compound or mixture and then anundiluted or full-strength sensitizing compound or mixture.

2. A process of sensitizing a stone plate or the like by applyingthereto a preparatory coating, then a priming of dilute sensitizingcompound or mixture, and finally an undiluted or full-strengthsensitizing compound or mixture.

3. A process of preparing sensitized plates stones or the like by firstcoating the same with a solution of silicate of potash and tannin inbeer, drying the same and when dry .priming the surface, after which itis salts, preparing such compound or composition in full strength, alike composition or compound greatly diluted, priming the surface to besensitized with the dilute compound or composition, and then coating itwith the compound or composition of full strength.

6. A process of sensitizing plates stones or the like by first coatingthe same with a solution of silicate of potash and tannin in beer,drying this first coating, priming the surface with a dilute compound orcomposition the base of which is gelatin, and then coating it with asensitive coating'of full-strength compound or composition the base ofwhich is gelatin sensitized by chrome salts.

In testimony whereof we have hereunto set our hands,in presence of twosubscribing witnesses, this 16th day of January, 1902.

GERALD FORTESGUE WETIIERMAN. GEORGE HOLZHAUSEN. Witnesses:

' BERNHARD DUKES,

JAMES I. LAWSON.

